Cathode heater



July 24, 1956 A. D. LA RUE CATHODE HEATER Filed Feb. 2, 1955 Sheets-Sheet l INVENTOR.

#45527 D. Lakuc A. D. LA RUE CATHODE HEATER July 24, 1956 2 Sheets-Sheet 2 Filed Feb. 2, 1955 United States Patent CATHODE HEATER Albert D. La Rue, Lexington, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application February 2, 1955, Serial No. 485,832

2 Claims. (Cl. 3'13337) This invention relates to a cathode heater and more particularly to an improved cathode heater for reducing cathode-cathode heater shorts due to heater sag.

Trouble from heater sag has been encountered in some types of electronic components where indirectly heated thoria cathodes are used. More particularly, there have been instances in some types of electronic components where indirectly heated thoria cathodes which operated satisfactorily with the cathode stem in a vertical position developed heater shorts when operated With the cathode stem in a horizontal position. Conventional cylindrically coiled cathode heaters have proven to be unsatisfactory for overcoming this deficiency.

The improved cathode heater of this invention is characterized by increased inherent mechanical rigidity. It is further characterized by a reduced diameter at its central portion to increase the clearance between the cathode heater and the inner wall of a thoria cathode emitting sleeve and since it is at the center of the cathode Where heater shorts are usually developed, this improvement markedly reduces heater shorts.

An object of this invention is to provide an improved cathode heater.

A further object is to provide an improved cathode heater characterized by reduced sag.

A further object is to provide an improved cathode heater characterized by increased mechanical rigidity and reduced sag under operating conditions.

A further object is to provide an improved cathode heater manifesting increased clearance at that portion prone to developing shorts with associated sleeve cathodes.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figs. 1 and 2 are an end view and is a plan view, respectively, of a cathode heater according to this invention,

Fig. 3 is a plan view of an assembled mandrel for winding the cathode heater shown in Figs. 1 and 2.

There is shown in Figs. 1 and 2 a circular open-coiled cathode heater 12. The cathode heater 12 is shown separate and apart from an electronic component since its manner of mounting is in accordance with generally accepted practice in this art. Between its cylindrical ends the coiled cathode heater 12 is reduced in diameter 2,756,362 Fatented July 24, 1956 to adjacent frustro-conical sections 14 and 16. The center of the heater coil is reduced to approximately one-half the diameter of the ends of the coil. The portion of reduced diameter occupies about one-half the total length of the heater coil.

The mandrel 18 for forming the heater coil includes a male mandrel portion 22 and a female mandrel portion 24. The male mandrel portion is reduced in the shape of a cone at 26 and includes an integral extension 28 of reduced diameter threaded at its end 32. The female mandrel portion 24 likewise includes a conical reduced portion 34 for disposition adjacent the conical reduced portion 26 of the male mandrel 22. The female mandrel is formed with a longitudinal bore 30 for registration with the extension 28 of reduced diameter of the male mandrel 22 and is retained thereon by nut 36. The male mandrel portion 22 is further formed with a transverse bore 38. Transverse bore 38 is provided for gripping an end of the heater coil wire during the forming of a heater coil.

In operation, the cathode heater coil of this invention with its central portion of reduced outside diameter is utilized in conventional manner in electronic components. Its reduced central portion increases rigidity and clearance thereby reducing heater shorts. Life tests performed on several horizontally-operated cathodes with cylindrical cathode heater coils have been compared with life tests with horizontally-operated cathodes heated by heater coils according to this invention. Greatly improved results have been obtained with a heater coil formed in accordance with this invention as compared to conventional cylindrical heater coils.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A cathode heater comprising an open coil of heater wire, said open coil being cylindrical at each end with both ends of equal outside diameter, the central portion of said coil between the ends thereof being in the form of a pair of identical frustro-conical portions in end-toend relationship whereby the longitudinal center of said coil has the smallest outside diameter.

2. In combination with an electronic element having an indirectly heated cathode, a cathode heater comprising an open coil of heater wire, said open coil being cylindrical at each end with both ends of equal outside diameter, the central portion of said coil between the ends thereof being in the form of a pair of identical frustoconical portions in end-to-end relationship whereby the longitudinal center of said coil has the smallest outside diameter.

References Cited in the file of this patent UNITED STATES PATENTS 1,716,645 Kuen June 11, 1929 2,454,765 Braunsdorfl? Nov. 30, 1948 2,479,193 Zabel Aug. 16, 1949 2,499,961 Lennox Mar. 7, 1950 2,717,325 Gosslar Sept. 6, 1955 

